relay_to

Optional boolean. Defaults to false. When set to true, allows relaying mail from anyone, so long as it is addressed to the requested domain.

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if domain == 'example.com' then
    return kumo.make_listener_domain {
      relay_to = true,
    }
  end
end)

Enable relaying based on SMTP authentication

This example shows how to use the connection metadata information to determine if the current session is authenticated, and use that to govern whether relaying is allowed.

In this example, any user is permitted to relay to anywhere:

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if conn_meta:get_meta 'authz_id' then
    -- We're authenticated as someone.
    -- Allow relaying
    return kumo.make_listener_domain {
      relay_to = true,
    }
  end
end)

A more sophisticated configuration might use a mapping to control which domains are allowed relaying based on the authorization id:

local RELAY_BY_DOMAIN = {
  ['example.com'] = {
    -- The user scott is permitted to relay to example.com
    ['scott'] = true,
  },
}

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  local dom_map = RELAY_BY_DOMAIN[domain]
  if dom_map then
    local authz_id = conn_meta:get_meta 'authz_id'
    if dom_map[authz_id] then
      return kumo.make_listener_domain {
        relay_to = true,
      }
    end
  end
end)